The present invention relates to a process for producing titanium dioxide by reacting titanium tetrachloride vapors with oxygen and to an improved reactor for use in such a system. The process and reactor of the present invention provides the ability to control properties, such as particle size, of the titanium dioxide product.
It is well-known that titanium tetrachloride reacts with oxygen in the vapor phase to form titanium dioxide and that this reaction is initiated by heating the reactants to a suitable temperature. However hot titanium tetrachloride is highly corrosive and therefore many useful materials of construction for heat exchangers used to heat titanium tetrachloride are rapidly corroded. In practice this generally imposes an upper limit of about 400° C. (752° F.) on the temperature to which titanium tetrachloride can be heated by conventional heat exchangers.
A suitable temperature for the reactants (oxygen and titanium tetrachloride) is about 950° C. (1742° F.) and, in order to achieve this temperature in known processes, the oxygen feed must be heated sufficiently to compensate for the above-mentioned relatively low titanium tetrachloride temperature. Frequently, oxygen is heated directly or heated by an electrical discharge to temperatures of about 1427-1871° C. (2600-3400° F.) as oxygen is introduced into the oxidation reactor in combination with an auxiliary fuel. The use of these methods introduce unwanted impurities such as, for example, carbonaceous residues from the fuel or metallic impurities from the electrodes used for the electrical discharge.